1. Field of the Invention
The invention relates to a measuring device for the measurement of the deformability of red blood corpuscles, erythrocytes, which device comprises a measurement chamber, which is subdivided by a foil into two chamber spaces, the foil having a passage opening, the diameter of which is smaller than the diameter, at rest, of a red blood corpuscle, the chamber spaces being formed in such a manner that a pressure gradient comes into existence between the two chamber spaces and thus a flow takes place from one chamber space to the other, and at least one electrode being disposed on each of the two sides of the foil in the region of the opening, each respective electrode being connected to an alternating voltage source.
2. Description of the Prior Art
A measuring device of the kind mentioned is known according to German Patent Specification No. 3,215,719. In order to measure the deformability of the erythrocytes, one of the chamber spaces of the measurement chamber is filled with a mixture of buffer solution and complete blood, and the other with buffer solution. Since a hydrostatic pressure gradient is present because of the channel course, the erythrocytes are caused to pass through the opening in the foil. In this connection, the time which the individual erythrocytes require in order to pass through a single-aperture membrane serves as a measure of the deformability. In the course of the passage of the erythrocyte through the opening of the foil, the total electrical resistance of the measurement chamber changes. This change is recorded; it is a direct measure of the passage time. An alternating voltage is applied under high-resistance conditions to the electrodes situated on both sides of the opening, and the total resistance--which changes during the passage of the erythrocyte through the opening--of the measurement cell is recorded in the form of a change in voltage.
A disadvantage in the case of the measurement of an alternating voltage is that the foil itself represents a capacitor, so that, in addition, a parasitic capacitive resistance is connected in parallel with the ohmic resistance of the opening. To this there are also added parasitic shunt capacities. An increase in the frequency does indeed lead to increasing resolution of the transit times, but the value of the capacitive resistance decreases. This results in a change--which becomes progressively smaller with increasing measurement frequencies--of the measurement signal on passage of the erythrocytes through the opening in the foil, so that a costly electronic analysis system becomes necessary.